The Bones of Copernicus

The Copernican principle—that Earth’s location, despite naive appearances, is not central in any cosmologically significant way—has been widely and persistently interpreted as entailing our planet’s “demotion” within the great scheme of things. When Hermann Bondi coined the phrase in the 1950s, the principle had already—since a century after Copernicus’s death—been read as implying Earth’s (and thus humankind’s) cosmic mediocrity. The author, a science historian, disputes this interpretation, showing instead how Earth’s planetary status, when first proposed, was viewed as a promotion. He goes on to discuss the Copernican principle in relation to the cosmological principle, an idea which was at first wed to the now abandoned steady-state cosmology, and describes its survival. History and literature from Aristotle to Dante to Galileo, as well as interviews with contemporary cosmologists, tell the story of how the Copernican principle arose and was eventually adapted to Big Bang cosmology, but is now increasingly under scrutiny. The interviews reveal that both the Copernican principle and the robust spirit that fired Copernicus’s achievement retain active if controversial roles in astrophysical thought.